The present invention relates to a combined forward-looking infrared/laser sensor. More particularly, the present invention relates to a targeting and imaging system that combines a mid-wave forward-looking infrared (FLIR) subsystem and a laser subsystem, including a laser range receiver (LRR) and a laser spot tracker (LST).
FLIR systems employ an array of infrared (IR) detectors for generating an image based on the IR emissions from a particular area of interest (AOI). In military applications, for example, the AOI may contain targets such as tanks, trucks, and/or other military vehicles or military hardware. These targets emit heat; therefore, they are typically warmer than their surrounding environment. Consequently, they can be distinguished in an IR image generated by a FLIR system.
The use of lasers in conjunction with FLIR systems is generally well known in the art. For example, lasers can be used to designate specific targets which are visible in a FLIR image. In one prior FLIR/laser system, laser energy is swept across a target that is visible in the FLIR image and used for the purpose of generating a 3-D image of the target. The 3-D image can, in turn, be used for target recognition and/or target classification (U.S. Pat. No. 5,345,304). In another prior FLIR/laser system, a laser is used for determining the range of a target from the FLIR/laser system""s host platform (U.S. Pat. No. 4,771,437). In yet another prior FLIR/laser system, a laser is used to determine the relative position and velocity of targets (U.S. Pat. No. 4,574,191). In addition, lasers have been used for the purpose of directing laser guided munitions to a desired target visible in a FLIR image.
In each of the aforementioned prior FLIR/laser systems, the ability of the FLIR/laser system to accurately recognize, detect, locate and/or track targets is dependent upon the ability of the system to maintain an accurate alignment between the FLIR and laser. Any fixed misalignment between the FLIR line-of-sight (LOS) and the laser LOS will result in laser overspill. As illustrated in FIG. 1, laser overspill is defined as the unintended amount of laser energy 110 that misses the target 105 and reflects off the background. Laser overspill is likely to result in range measurement error, as illustrated by Rerr in FIG. 2. False range information, in turn, will result in less accurate target recognition, detection, location, and velocity information, as well as less accurate weapon guidance data.
Boresighting is a common term of art which refers to the process of aligning the LOS of a given system. Prior designs, such as the Low Altitude Night Terrainxe2x80x94following Infrared Navigation (LANTIRN) system, employ boresighting processes to minimize fixed alignment errors between the FLIR LOS and the laser LOS. Boresighting processes typically involve optical and/or mechanical realignment of, for example, the FLIR LOS and the laser LOS. Moreover, boresighting processes may be manual or they may be automatic. As stated, boresighting processes are generally well known in the art.
Unfortunately, the alignment error between, for example, a FLIR LOS and a laser LOS is not necessarily a fixed error. In military applications, FLIR/laser based systems are typically installed on moving platforms, such as tactical aircraft (e.g., an F-15 or an F-16). These platforms subject the FLIR/laser based system to large mechanical forces and vibrations. These forces and vibrations directly act upon the optical components which govern the FLIR LOS and the laser LOS. Moreover, FLIR LOS and laser LOS displacements about the pitch axis appear to have the most detrimental affect on system performance (i.e., the ability to accurately recognize, detect, locate and/or track targets).
As illustrated in FIG. 3, prior designs such as LANTIRN employ a separate FLIR optics pitch bearing 205 and laser optics pitch bearing 210, as well as a separate FLIR aperture 215 and laser aperture 220. Consequently, the aforementioned mechanical forces and vibrations acting upon the FLIR/laser based system will cause the FLIR LOS and the laser LOS to nutate about the pitch axis independent of each other, resulting in LOS jitter and a dynamic (i.e., continuously changing) FLIR LOS-to-laser LOS alignment error in addition to any exiting fixed alignment error. Although the boresighting processes mentioned previously can be used to correct fixed alignment errors, they are generally ineffective with respect to correcting dynamic alignment errors.
Yet another problem associated with prior systems such as LANTIRN, which may significantly contribute to LOS alignment errors, is the fact that FLIR images rotate about the roll axis as a function of gimbal pitch angle. To compensate for this anomaly, prior designs such as LANTIRN counter-rotate the entire FLIR detector assembly. However, FLIR detector assemblies are relatively large, and rotating a large mass to counter rapidly changing gimbal pitch angles has many disadvantages. First and foremost, it is very difficult to counter-rotate a large mass with sufficient response time to compensate for high speed pitch rotations. The inability to compensate for high speed pitch rotations can result in additional FLIR LOS-to-laser LOS alignment errors. Second, the wires which connect to the FLIR detector array elements must pass through a rotating interface. Rotating the interface and the wires passing through the interface significantly impacts system reliability.
The present invention is a high resolution, gimbaled mid-wave FLIR/laser based system which comprises an electro-optic subsystem that is designed to minimize FLIR LOS-to-laser LOS alignment errors, including fixed alignment errors and dynamic alignment errors, so as to provide more accurate target recognition, detection, location and/or tracking information. If used in conjunction with a military weapon delivery system, these performance enhancements translate into greater survivability for the host platform which can now release its weapons at longer (i.e., safer) standoff ranges in hostile environments.
In addition, the present invention comprises a number of other subsystems and subsystem capabilities which support and further enhance the effectiveness of the electro-optics subsystem. For example, the present invention comprises a single processing subsystem which provides a number of important and novel image processing and image preprocessing functions including: a xe2x80x9cdeadxe2x80x9d detector cell replacement function, a scene-based pattern removal function, a 2-D sharpen filter, a dynamic range control function, and a 2xc3x97 image enhancement function which employs a unique subpixel dithering process.
The present invention also comprises a novel fault isolation subsystem. The fault isolation subsystem is capable of distinguishing fault conditions which arise in the amplifier portions of the various servo systems from fault conditions which arise in the servo motor portion of the servo systems. Thus maintenance personnel need only remove and replace the defective portion of a servo system without having to remove and replace the entire servo system.
Finally, the present invention comprises a novel electromagnetic interference (EMI) grid. This grid more thoroughly prevents undesired energy from entering the system and interfering with electrical signals. The grid also prevents undesired energy generated by the system to radiate, thereby interfering with the operation of other systems in close proximity.
It is an object of the present invention to provide a high resolution, FLIR/laser based targeting and imaging system.
It is another object of the present invention to provide a high resolution FLIR/laser based system that minimizes alignment errors between the FLIR LOS and the laser LOS.
It is yet another object of the present invention to minimize alignment errors, caused by FLIR LOS and laser LOS jitter by providing a single pitch bearing and a common aperture for both the FLIR optics and the laser optics.
It is still another object of the present invention to minimize alignment errors, caused by the rotation of the FLIR image about the roll axis when the pitch/yaw gimbal is rotated about the pitch axis, by counter-rotating a deroll prism optic rather than the FLIR detector assembly.
It is another object of the present invention to filter undesirable electromagnetic energy from the IR energy entering the system aperture.
It is still another object of the present invention to provide a number of signal processing functions which further enhance the quality of the FLIR image.
Finally, it is an object of the present invention to provide a fault detection process that accurately isolates fault conditions and limits the removal and replacement of hardware that is otherwise functioning properly.
The aforementioned and other objects of the present invention are achieved by a targeting and imaging system that comprises a forward-looking infrared (FLIR) optical subsystem which receives infrared (IR) energy from an area of interest (AOI), and which generates an IR image of the AOI. The system also includes a laser optical subsystem for generating laser energy which illuminates at least one object in the AOI, and which receives laser energy reflected by the at least one object. Furthermore, the laser optical subsystem and the FLIR optical subsystem share a common pitch bearing.
The aforementioned and other objects of the present invention are also achieved by a targeting and imaging system that comprises a forward-looking infrared (FLIR) optical system for receiving infrared (IR) energy from an area of interest (AOI), and a FLIR optical imager for generating an IR image with the IR energy received from the AOI. The FLIR optical imager is arranged to receive the IR energy from the FLIR optical system. The system also includes a laser transmitter, a laser receiver, and laser optics for directing laser energy from the laser transmitter to a desired target located in the AOI, and for directing laser energy returning from the desired target in the AOI to the laser receiver. Furthermore, the FLIR optical system and the laser optics share a common pitch bearing, such that all optical elements individually subject to pitch rotations are commonly shared by the FLIR optical system and the laser optics.
The aforementioned and other objects of the present invention are also achieved by a targeting and imaging system that comprises forward-looking infrared (FLIR) optics for steering an infrared (IR) line-of-sight (LOS) towards a desired area of interest (AOI), for receiving IR energy from the AOI, for focusing the IR energy, and for generating an optical image of the AOI. The system also includes a laser transmitter, a laser range receiver (LRR), a laser spot tracker (LST), and laser optics for steering a laser LOS, such that the transmitted laser energy illuminates at least a portion of the AOI, for receiving laser energy, and for directing the received laser energy into the LRR and the LST. In addition, the FLIR optics means and the laser optics means share a single pitch bearing, and the IR energy and the laser energy pass through a common aperture.
The aforementioned and other objects of the present invention are also achieved by a targeting and imaging system that includes LOS correction means for adjusting an IR LOS and a laser LOS, and for minimizing LOS alignment errors between the IR LOS and the laser LOS.
The aforementioned and other objects of the present invention are also achieved by a targeting and imaging system that includes fault isolation means for isolating an electrical fault in a servo system comprising a servo motor and an amplifier.
The aforementioned and other objects of the present invention are also achieved by a targeting and imaging system that includes a boresight subsystem.
The aforementioned and other objects of the present invention are also achieved by a targeting and imaging system that includes a signal processing subsystem.
The aforementioned and other objects of the present invention are also achieved by a targeting and imaging system that is contained within a housing that includes a window through which IR and laser energy passes.